This invention is based on the attempt to fulfill several requirements for a new lock.
First there is a need for an easily changed internal combination of the lock so that the key can be easily changed. This is particularly needed in hotels or with safe-deposit boxes in banks. In certain critical uses of dial operated safes it is often required that the combination be changed at regular intervals.
Secondly there is always a need to make the lock as simple and as inexpensive as possible.
Thirdly there is a need to make the lock as small as possible, without sacrificing ruggedness and ease of manufacture.
Fourthly the lock should be difficult to pick, that is, to be opened without the use of the correct key and without inflicting any damage to the lock.
Fifth the lock should be such that a very large number of different keys, or dial combinations, should be available.
I believe that the various embodiments of my invention meet the above criteria.
I am aware that the prior art shows locks where a change of key is readily accomplished. Such locks may contain an easily replaceable key cylinder. In other designs, the keysettable elements are themselves modified. See, for example U.S. Pat. No. 3,837,196. In some cases, the key itself can be changed by cooperation with the lock. An example of this is U.S. Pat. No. 3,868,196.
Two patents that are much closer to the subject of my invention are U.S. Pat. Nos. 3,555,858 and 3,167,944.
In U.S. Pat. No. 3,167,944 to Pickering, there are shown two "permutation strips" that have fins 36 that, in turn, are images of the key (see FIG. 7). The two strips are complimentary to each other so that a plurality of "slides" will be shifted by the key so that they will be properly positioned between the two strips and the lock will then be opened. It should be noted that the two opposite edges of the key have to be complimentary to each other, and both are complimentary to the two permutations strips. This is a limitation on the number of different keys that can be used with this lock. Also the need for two closely related exchangeable strips adds to the cost and complexity of the device.
U.S. Pat. No. 3,555,858 shows another device where a "slug" component complimentary to the desired key is designed to permit the change of a key by changing this component. Each "Slotted Plate" 66 is pulled by a spring 112 to the right as viewed in FIG. 6 or FIG. 4. Thus, when the key is pressed against the slotted plates 66, they will attain their correct position for the lock to open. Because the sliding "slotted plates" 66 have many notches, many different keys can be accomodated. In this lock the number of different keys that can be made for the lock depends on the number and position of the notches, or slots, in the sliding plates 66.
The art of changeable locks is quite extensive. The two locks mentioned above are merely examples. In the case of conventional dial-operated combination locks, a series of discs are rotated. Each disc is usually provided with a notch so that when all of the discs are properly set, the notches are aligned, and a "fence" is able to enter the aligned notches. This permits the lock to open. In changeable combination locks, the discs are usually made of two concentric components. The outer component carries the usual notch. The other component, usually of smaller diameter, carries the interlocking or driving pins that co-operate with another disc. The two components normally rotate as one unit. When it is desired to change the combination, the two components are released from each other and the relationship between the notch and the driving pins can be altered. After this the two parts are locked to each other again, and rotate as one unit.
My invention can make use of a particular form of a combination lock where the usual discs are replaced by a set of concentric rings. The rings are interlocked exactly in the same manner as discs in a more conventional lock. Such a lock is on display in the lock museum of the Sargent and Greenleaf Company in Kentukee. I shall explain this lock in greater detail in one embodiment of any invention.